In video processing and storage applications, digital video data is typically encoded to conform to the requirements of a known standard. One such widely adopted standard is the MPEG2 (Moving Pictures Expert Group) image encoding standard, hereinafter referred to as the "MPEG standard". The MPEG standard is comprised of a system encoding section (ISO/IEC 13818-1, Jun. 10, 1994) and a video encoding section (ISO/IEC 13818-2, Jan. 20, 1995, hereinafter referred to as the "MPEG systems standard" and "MPEG video standard" respectively. Video data encoded to the MPEG standard is in the form of a packetized datastream which typically includes the data content of many program channels (analogous to channels 1-125 in cable TV, for example). The data content of premium program channels such as HBO.TM., Cinemax.TM. and Showtime.TM., for example, is usually protected from unauthorized access by methods such as encryption and scrambling. These methods may be used alone, repetitively, or in combination to provide a plurality of levels of protection.
In a decoder, access to the premium channels is typically governed by a conditional access system which manages user billing and controls program descrambling and decryption based on user entitlement. The conditional access system may determine whether access is authorized in a variety of ways. For example, authorization may be determined within the decoder from user entitlement information pre-programmed on a so-called "smart card". Alternatively, authorization may be determined at a remote location and implemented within the decoder using user entitlement information that is transmitted from the remote location, as in a cable television pay-per-view service. The entitlement information typically includes codes used to generate descrambling and decryption keys that are used for program descrambling and decryption. However, the entitlement information may instead include the keys themselves.
The processing of encrypted and non-encrypted program data and the management of associated encryption and scrambling codes for storage, billing and other applications presents a number of problems. One problem is presented by the need to maintain encryption code security when a program is stored by a consumer in either encrypted or non-encrypted form for viewing at a later time. Further problems are involved in providing a system that permits billing on the storage or playback of a program and that permits copy protected processing of encrypted and non-encrypted program data.
These problems are addressed by a system according to the present invention. Hereinafter the term "encryption" encompasses scrambling functions to the extent that the functions are used to prevent unauthorized use.